1. Field of the Invention
The present invention relates to a fuel cell stack and a method of producing the same. In particular, the present invention relates to a fuel cell stack that includes separators formed of a metal plate and a method of producing the same.
2. Description of the Related Art
Solid polymer fuel cells include a solid polymer electrolyte membrane having proton conductivity. In such solid polymer fuel cells, a fuel gas is supplied to an anode, which is one of a pair of electrodes provided so as to sandwich the electrolyte membrane, and an oxidizer gas is supplied to a cathode, which is another electrode. Solid polymer fuel cells generate electric power utilizing electrochemical reactions caused on the surfaces of the electrolyte membrane.
Such a fuel cell is composed of cells as described below, and the cells, the number of which is related to the required output voltage, are arrayed in a line. The total output power generated by the cells of the fuel cell is obtained from the powers of the cells connected in series.
Each of the cells of the fuel cell includes a membrane electrode assembly (MEA) in which an electrolyte membrane is sandwiched between a pair of electrode catalyst layers, and separators which constitute gas flow paths disposed at each side of the membrane electrode assembly.
Each of the separators constitutes a gas flow path through which a fuel gas or an oxidizer gas flows, and also constitutes a flow path through which a temperature-control medium flows.
The entire separators are made of a conductive material because the separators also function as a conductive path for obtaining the output from the electrode catalyst layers of each cell of the fuel cell.
Hitherto, separators used for a fuel cell were made of carbon, which has both corrosion resistance and conductive properties. Recently, however, metal separators have been used to reduce the cost of the fuel cell, and to reduce the thickness of the separator to improve the output density.
Japanese Unexamined Patent Application Publication No. 2005-190968 discloses a metal separator produced by plating a noble metal layer, which serves as a corrosion-resistant coating layer, on a surface of a stainless steel plate.